Natural Resources — Soil, Water, Air, Forests & Waste | CTET Science P2

The Nitrogen Cycle

Nitrogen makes up about 78% of Earth's atmosphere, yet most living organisms cannot use free atmospheric nitrogen (N₂) directly. The nitrogen cycle is the biogeochemical process by which nitrogen is converted into various forms as it circulates through the atmosphere, terrestrial and aquatic ecosystems.

Key processes in the nitrogen cycle:

• Nitrogen Fixation: Conversion of atmospheric N₂ into ammonia (NH₃) or nitrates (NO₃⁻) usable by plants. Done by: (a) free-living bacteria like Azotobacter in soil; (b) symbiotic bacteria Rhizobium in root nodules of leguminous plants (peas, beans, clover); (c) lightning (non-biological).
• Nitrification: Conversion of ammonia into nitrites (by Nitrosomonas) and then nitrates (by Nitrobacter). Plants absorb nitrates directly.
• Assimilation: Plants absorb nitrates from soil to make amino acids and proteins; animals get nitrogen by eating plants or other animals.
• Ammonification: Decomposition of dead organic matter by bacteria and fungi, releasing ammonia back into the soil.
• Denitrification: Conversion of nitrates back into atmospheric N₂ by anaerobic bacteria (e.g., Pseudomonas) in waterlogged soils.

The distinction between nitrogen fixation (atmospheric N₂ → usable form) and nitrification (ammonia → nitrates) is a common CTET question. Excess fertilisers can cause eutrophication — excess nitrates enter water bodies, causing algal bloom that depletes oxygen and kills aquatic life. Bio-magnification occurs when harmful substances like pesticides accumulate at higher trophic levels. Soil erosion and nitrification are effects of overuse of fertilisers, but nitrification itself is a natural soil process — it is NOT a harmful consequence of fertiliser overuse (CTET Jul 2024).

Types of Soil and Their Properties

Soil is the uppermost layer of the Earth's crust and is essential for plant growth. It is formed by the weathering of rocks over thousands of years. Soil composition: mineral particles (~45%), organic matter/humus (~5%), water (~25%), and air (~25%).

Soil Profile — a vertical cross-section of soil reveals distinct layers called horizons:

• Horizon A (Topsoil): Richest in humus and nutrients; supports most plant roots.
• Horizon B (Subsoil): Less humus; accumulates minerals leached from above.
• Horizon C (Parent rock/Regolith): Partially weathered rock.
• Horizon D (Bedrock): Unweathered solid rock.

Types of soil based on particle size:

• Sandy soil: Large particles; high aeration; low water retention; not very fertile.
• Clayey soil: Very fine particles (smallest); high water retention; poor aeration; can be fertile but heavy; waterlogged easily. Note: clayey soil is LESS aerated than loamy soil — a common CTET trap question.
• Loamy soil: Ideal mixture of sand, clay, and silt; moderate water retention; good aeration; highest fertility; best for agriculture.
• Silty soil: Smooth texture; moderate fertility; found near river beds.

Humus (decomposed organic matter) increases soil fertility, water retention, and improves soil structure. Microorganisms in soil (bacteria, fungi, earthworms) decompose organic matter and recycle nutrients. Soil erosion — removal of topsoil by water and wind — is accelerated by deforestation and overgrazing. Soil conservation measures include: afforestation, contour ploughing, terracing, and maintaining ground cover.

Water — Sources, Conservation and Rainwater Harvesting

Water is essential for all life on Earth. About 71% of Earth's surface is covered by water, but only about 2.5% is freshwater — and of that, most is locked in ice caps and glaciers. Only about 0.3% of total freshwater is accessible in rivers, lakes, and groundwater.

Sources of water:

• Surface water: Rivers, lakes, ponds, and reservoirs.
• Groundwater: Found in underground aquifers, accessed via wells and borewells.
• Rainwater: The ultimate source of all freshwater on land.

Water scarcity is caused by: overuse, pollution, unequal distribution, and climate change altering rainfall patterns. Growing populations and industrial demand have worsened the freshwater crisis.

Rainwater Harvesting is the collection and storage of rainwater for future use. Benefits:

• Recharges groundwater aquifers (conserves groundwater).
• Reduces surface runoff and therefore local flooding.
• Can be used for irrigation of crops.
• Reduces demand on municipal water supply.
• It does NOT create drainage problems — this is a CTET distractor (CTET Jul 2024).

Methods of rainwater harvesting include: rooftop harvesting (directing rainwater from rooftops into storage tanks or recharge pits), check dams, and percolation ponds.

Traditional water conservation practices in India include: kunds, johads, baolis (stepwells), tanks (eri), and bamboo drip irrigation (Meghalaya). The water table rises with increased rainwater harvesting and falls with excessive borewell extraction.

Air — Composition and Pollution

Air is a mixture of gases that makes up Earth's atmosphere. Its approximate composition by volume: Nitrogen 78%, Oxygen 21%, Argon 0.93%, Carbon dioxide 0.04%, and trace amounts of other gases plus water vapour.

Functions of atmospheric layers:

• Troposphere: Nearest to Earth; contains weather; where we breathe.
• Stratosphere: Contains the ozone layer that absorbs harmful UV radiation.
• Mesosphere: Burns up meteors.
• Thermosphere/Ionosphere: Reflects radio waves; auroras occur here.

Air Pollution is the presence of harmful substances in the atmosphere. Major pollutants:

• Carbon monoxide (CO): Incomplete combustion; toxic, binds to haemoglobin.
• Sulphur dioxide (SO₂): From burning coal; causes acid rain and respiratory problems.
• Nitrogen oxides (NOₓ): From vehicles and industries; cause smog and acid rain.
• Particulate matter (PM2.5, PM10): Fine particles from vehicles, construction, burning — cause serious respiratory and cardiovascular diseases.
• Chlorofluorocarbons (CFCs): From refrigerants and aerosols; destroy the ozone layer.

Effects of air pollution: respiratory diseases, cardiovascular disease, acid rain, ozone depletion, global warming, and reduced visibility (smog). Control measures include: catalytic converters in vehicles, smokeless chulhas, switching to CNG, clean coal technology, stricter emission norms, and afforestation.

The greenhouse effect is the natural warming of Earth due to CO₂, methane, and water vapour trapping heat. Global warming refers to the enhanced greenhouse effect caused by excessive CO₂ emissions from fossil fuels.

Forests — Importance and Conservation

Forests are one of the most vital natural resources — they cover about 31% of Earth's land area and provide countless ecological, economic, and social services.

Ecological importance of forests:

• Produce oxygen and absorb CO₂ — act as carbon sinks.
• Regulate the water cycle — promote rainfall and recharge groundwater.
• Prevent soil erosion and maintain soil health.
• Regulate local and global climate (temperature, humidity).
• Provide habitat for millions of species — support biodiversity.
• Act as natural filters for air and water.

Economic importance: Forests provide timber, firewood, medicinal plants, non-timber forest products (NTFP) like honey, bamboo, resins, gum. Forest-dependent communities rely on forests for food and livelihood.

Threats to forests: Deforestation (for agriculture, urbanisation, logging), forest fires, over-exploitation, and climate change. India loses significant forest cover each year to infrastructure and agricultural expansion.

Conservation measures:

• Afforestation: Planting trees on degraded land.
• Reforestation: Replanting cleared forest areas.
• Social Forestry: Involving communities in planting and protecting trees.
• Protected Areas: National Parks, Wildlife Sanctuaries, Biosphere Reserves.
• Joint Forest Management (JFM): Collaborative management between government and local communities.
• Van Mahotsav: Annual tree-planting festival in India launched in 1950.

The Chipko Movement (1970s, Uttarakhand) was a grassroots movement where villagers, especially women, hugged trees to prevent logging. It is a landmark example of community-based forest conservation. ENVIS (Environmental Information System) and Wildlife Protection Act 1972 are key legal frameworks for forest conservation in India.

Biodegradable vs Non-Biodegradable Waste

Waste generated by human activities can be broadly classified based on whether microorganisms can break it down into simpler, harmless substances.

Biodegradable waste can be decomposed naturally by bacteria, fungi, and other microorganisms. Examples: food scraps, vegetable peels, leaves, paper, cotton cloth, wood, cow dung. These materials cycle back into the environment relatively quickly.

Non-biodegradable waste cannot be broken down by natural processes and persists in the environment for years or centuries. Examples: plastic bags, synthetic fibres, glass, metals, pesticides (like DDT), nuclear waste.

Approximate decomposition times (important for CTET):

• Banana peel: 10–30 days
• Cotton shirt: 1–2 weeks (some sources say months)
• Silk scarf: 2–5 months (silk is a protein fibre, slower than cotton)
• Paper: 4 years (treated paper with bleach decomposes slowly)
• Plastic bottle: Several hundred years (CTET maps this to 'several years' as the longest category in comparison sets)

Bio-magnification (Biomagnification): The increase in concentration of a toxic substance (e.g., DDT, mercury) as it moves up the food chain. A small fish accumulates pesticides; a larger fish eats many small fish and concentrates the pesticide further; a bird at the top of the food chain has the highest concentration. This is why fish-eating birds like eagles were severely affected by DDT.

The distinction between biodegradable and non-biodegradable waste is the basis for effective waste segregation at source — a key practice in solid waste management recommended in India's Solid Waste Management Rules 2016.

Waste Management and the 3Rs

Effective waste management is essential to reduce pollution, conserve resources, and protect human health. The 3Rs framework — Reduce, Reuse, Recycle — provides a hierarchy of waste management strategies.

• Reduce: The most effective approach — minimise waste generation at the source. Buy only what is needed; avoid single-use plastics; choose products with minimal packaging.
• Reuse: Use items more than once before discarding. Use cloth bags instead of plastic bags; repair electronics instead of replacing; use refillable bottles.
• Recycle: Process waste materials into new products. Paper, glass, metal, and certain plastics can be recycled. Recycling conserves raw materials and energy but requires infrastructure and sorting.

Additional strategies: Recover energy from waste (waste-to-energy plants) and Refuse unnecessary items. Some frameworks extend to the 5Rs or even 7Rs.

Composting is the controlled decomposition of organic biodegradable waste (kitchen waste, garden waste) by microorganisms to produce compost — a nutrient-rich soil amendment. Vermicomposting uses earthworms (e.g., Eisenia fetida) to speed up decomposition.

Landfills are designated sites for waste disposal. Sanitary landfills contain waste with liners to prevent leachate from contaminating groundwater. Landfill gas (mainly methane) can be captured for energy.

Incineration reduces volume of waste and can generate energy, but produces ash and air pollutants including dioxins if not properly managed.

India's Swachh Bharat Mission aims to improve solid waste management across urban and rural India. E-waste (electronic waste) must be handled separately as it contains toxic materials like lead, mercury, and cadmium.

Sustainable Use of Natural Resources

Sustainability means meeting the needs of the present generation without compromising the ability of future generations to meet their own needs (Brundtland Commission, 1987). This principle applies to all natural resources — soil, water, air, forests, minerals, and biodiversity.

Threats to sustainable use:

• Rapid population growth increasing demand for resources.
• Industrialisation and urbanisation depleting non-renewable resources.
• Over-exploitation of fisheries, forests, and groundwater.
• Chemical pollution degrading soil and water quality.

Strategies for sustainable resource use:

• Renewable energy: Solar, wind, hydro, and geothermal energy instead of fossil fuels.
• Organic farming: Reduces dependence on chemical fertilisers and pesticides; maintains soil health.
• Integrated pest management (IPM): Uses biological controls and minimal chemicals.
• Water conservation: Drip irrigation, rainwater harvesting, and fixing leaks reduces water wastage.
• Biodiversity conservation: Protects ecosystems that provide essential services.

Key international frameworks:

• Earth Summit, Rio de Janeiro (1992): Convention on Biological Diversity (CBD) and UNFCCC signed.
• Kyoto Protocol (1997): Binding emission reduction targets for developed nations.
• Paris Agreement (2015): Aimed to limit global warming to 1.5–2°C above pre-industrial levels.
• Sustainable Development Goals (SDGs): 17 goals adopted by UN in 2015 to be achieved by 2030.

In the classroom, sustainable development can be taught through activities like maintaining a school garden, conducting energy audits, and practising waste segregation. These develop environmental consciousness and responsible citizenship — key objectives of science education at the upper primary level.